1. Field of the Invention
This invention relates generally to digital circuits for processing signals and more specifically to circuits for providing a multiple function interface to a central processing unit.
2. Brief Description of the Prior Art
Various devices have been heretofore proposed for the purpose of determining the position of a movable element by processing the pulse signal outputs of an electro-optical transducer for applications such as weight measuring environments. Examples of such prior devices are illustrated in U.S. Pat. No. 2,886,717 and U.S. Pat. No. 3,487,399.
Earlier signal processing and counting systems employed RC networks which were time and temperature dependent and did not provide well defined pulse widths. Additionally, these systems were highly susceptible to both internal and external noise which resulted in generally poor reliability.
While the signal processing system illustrated in U.S. Pat. No. 4,143,364 issued to the patentee of the present invention, provided reliable signal processing in a weight measuring environment and adapted to optically define true scale zero displacement in an unambiguous manner, various drawbacks have been encountered in transmitting counter data to microprocessing means for processing. The microprocessor was required to perform numerous calculations in determining the article weight from the counter data including the averaging of counter readings and unit conversion from displacement counts to weight units. Further, the microprocessor performed computations to determine postage based upon weight and article destination. Traditionally, such microprocessors utilized separate registers for addressing and data lines which provided inherent limitations in input/output capabilities. With limited register space, the microprocessor was required to rapidly unload counter data, because new counter data was entering. Further, there was a hazard that count data might be unloaded into the microprocessor during propagation of a count.